Robotic devices have led to major advances in understanding the motor control of neurologically intact and neurologically impaired individuals. While many studies have used robotic devices to study upper limb motor adaptation and control, there are relatively few robotic devices for studying the lower limb. Ferris and colleagues have developed robotic lower limb orthosis to study motor adaptation during human locomotion. Initial studies indicate that humans can substantially adapt the timing and magnitude of lower limb muscle activation patterns to walk with near normal kinematics while being assisted by the robotic orthosis. The ability to use upper limbs to control lower limb robotic orthosis could greatly facilitate locomotor rehabilitation in individuals with neurological impairment. This novel control method would give the patient direct control over timing and magnitude of the robotic assistance. However, it is not known if humans can readily adapt upper limb muscle activity to effectively control lower limb robotic assistance during walking. Therefore, the overall objectives of the proposed research are to determine 1) if humans will modify upper limb muscle activity and/or movement during treadmill walking to control plantar flexion assistance from a robotic ankle-foot orthosis (AFO), and 2) if one controller allows the user to adapt faster or gain more assistance from the AFO than the other controllers. We will have healthy human subjects walk while wearing a robotic AFO powered by an artificial plantar flexor muscle controlled by the upper limb. We will test 3 different proportional control methods for the robotic AFO: myoelectric control using the triceps muscle, kinematic control using elbow extension, and a handheld pushbutton. Our primary variable will be net mechanical work done by the AFO during push-off. This will allow us to quantify how well the AFO can assist the subject during walking. We will also test for differences between controllers in terms of speed of motor adaptation. We will calculate motor adaptation period by the time required to reach steady state in: a) ankle kinematic correlation coefficient, b) orthosis positive work and c) orthosis negative work. To further characterize how subjects modify their muscle activation and/or movement, we will also analyze lower limb muscle activity, kinematics, and kinetics. The results of these studies could lead to better robotic interfaces for assisting gait rehabilitation after spinal cord injury, stroke, or other neurological impairments. [unreadable] Lay summary: The insight into the neural control of human locomotion and motor adaptation provided by this study may translate into innovative rehabilitation therapies and major advances in powered orthoses and prostheses for individuals with impaired mobility due to neurological injury or amputation. [unreadable] [unreadable] [unreadable] [unreadable]